Conventionally, a hot and cold water mixing valve has been used for controlling a temperature of a mixture of hot and cold water by biasing a movable valve for changing a mixture ratio of hot water to cold water by means of a spring made of a shape memory alloy whose spring coefficient changes with temperature. Such a hot and cold water mixing valve is disclosed in Patent Document 1, for example. Here, a structure of the hot and cold water mixing valve disclosed in Patent Document 1 will be shown in and described with reference to FIG. 4.
As shown in FIG. 4, the hot and cold water mixing valve in Patent Document 1 employs a structure in which a cylindrical casing 3 is provided with a control valve mechanism. A hot water inlet a through which hot water flows and a cold water inlet b through which cold water flows are formed at a cylinder wall of the casing 3 and arranged in parallel in an axial direction. A hot water valve seat 3a is formed in a position inside the hot water inlet a, and a cold water valve seat 3b is formed in a position inside a cold water inlet. Further, a mixing chamber 13 which communicates with the hot water inlet a and the cold water inlet b is formed at one end of the casing 3. A temperature adjusting means 330 which is subjected to temperature setting by a user is formed at another end.
A control valve member 300 which is movable in an axial direction of the casing is incorporated between the hot water valve seat 3a and the cold water valve seat 3b which are formed in the casing 3. This control valve member 300 whose one end is subjected to a load of a bias spring 310 which is in abutment with the temperature adjusting means 330 and whose other end is subjected to a load of a spring 320 (temperature sensitive spring) which is made of a shape memory alloy and disposed in the mixing chamber 13 changes an opening/closing ratio between the hot water inlet a and the cold water inlet b by balancing between the loads applied by the bias spring 310 and the temperature sensitive spring 320.
Then, a user operates the temperature adjusting means 330 and adjusts a position of the control valve member 300 to thereby change the opening/closing ratio between the hot water inlet and the above-mentioned cold water inlet and to set up a temperature of mixed water to be discharged from the hot and cold water mixing valve. Further, for example, in a situation where a desired temperature is set up by the temperature adjusting means 330, it is assumed that the temperature of the mixed water in the mixing chamber 13 rises since a flow rate of the incoming water decreases etc., due to a hydraulic pressure drop etc. In this case, the temperature sensitive spring 320 disposed in the mixing chamber 13 acts to increase the generating load to move the position of the control valve member so that the temperature of the mixed water is controlled by changing the opening/closing ratio between the hot water inlet and the cold water inlet.    Patent Document 1: Japanese Patent Application Publication No. 2006-307971